+#define __PACKAGE__ "Variable::Magic"
+
+#define R(S) fprintf(stderr, "R(" #S ") = %d\n", SvREFCNT(S))
+
+#define PERL_VERSION_GE(R, V, S) (PERL_REVISION > (R) || (PERL_REVISION == (R) && (PERL_VERSION > (V) || (PERL_VERSION == (V) && (PERL_SUBVERSION >= (S))))))
+
+#define PERL_VERSION_LE(R, V, S) (PERL_REVISION < (R) || (PERL_REVISION == (R) && (PERL_VERSION < (V) || (PERL_VERSION == (V) && (PERL_SUBVERSION <= (S))))))
+
+#ifndef VMG_PERL_PATCHLEVEL
+# ifdef PERL_PATCHNUM
+# define VMG_PERL_PATCHLEVEL PERL_PATCHNUM
+# else
+# define VMG_PERL_PATCHLEVEL 0
+# endif
+#endif
+
+#define VMG_HAS_PERL_OR(P, R, V, S) ((VMG_PERL_PATCHLEVEL >= (P)) || (!VMG_PERL_PATCHLEVEL && PERL_VERSION_GE((R), (V), (S))))
+
+#define VMG_HAS_PERL_AND(P, R, V, S) (PERL_VERSION_GE((R), (V), (S)) && (!VMG_PERL_PATCHLEVEL || (VMG_PERL_PATCHLEVEL >= (P))))
+
+/* --- Compatibility ------------------------------------------------------- */
+
+#ifndef Newx
+# define Newx(v, n, c) New(0, v, n, c)
+#endif
+
+#ifndef SvMAGIC_set
+# define SvMAGIC_set(sv, val) (SvMAGIC(sv) = (val))
+#endif
+
+#ifndef mPUSHi
+# define mPUSHi(I) PUSHs(sv_2mortal(newSViv(I)))
+#endif
+
+#ifndef dMY_CXT
+# define dMY_CXT
+# undef MY_CXT
+# define MY_CXT vmg_globaldata
+# undef START_MY_CXT
+# define START_MY_CXT STATIC my_cxt_t MY_CXT;
+# undef MY_CXT_INIT
+# define MY_CXT_INIT
+# undef MY_CXT_CLONE
+# undef aMY_CXT
+# undef pMY_CXT
+# define VMG_THREADSAFE 0
+#else
+# define VMG_THREADSAFE 1
+#endif
+
+#ifndef PERL_MAGIC_ext
+# define PERL_MAGIC_ext '~'
+#endif
+
+#ifndef MGf_COPY
+# define MGf_COPY 0
+#endif
+
+#ifndef MGf_DUP
+# define MGf_DUP 0
+#endif
+
+#ifndef MGf_LOCAL
+# define MGf_LOCAL 0
+#endif
+
+/* uvar magic and Hash::Util::FieldHash were commited with p28419 */
+#if VMG_HAS_PERL_AND(28419, 5, 9, 4)
+# define VMG_UVAR 1
+#else
+# define VMG_UVAR 0
+#endif
+
+#if !defined(VMG_COMPAT_ARRAY_PUSH_NOLEN) && VMG_HAS_PERL_OR(25854, 5, 9, 3)
+# define VMG_COMPAT_ARRAY_PUSH_NOLEN 1
+#else
+# define VMG_COMPAT_ARRAY_PUSH_NOLEN 0
+#endif
+
+/* since 5.9.5 - see #43357 */
+#if VMG_HAS_PERL_OR(31473, 5, 9, 5)
+# define VMG_COMPAT_ARRAY_UNDEF_CLEAR 1
+#else
+# define VMG_COMPAT_ARRAY_UNDEF_CLEAR 0
+#endif
+
+#if VMG_HAS_PERL_OR(32969, 5, 11, 0)
+# define VMG_COMPAT_SCALAR_LENGTH_NOLEN 1
+#else
+# define VMG_COMPAT_SCALAR_LENGTH_NOLEN 0
+#endif
+
+#if VMG_UVAR
+
+/* Bug-free mg_magical - see http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-01/msg00036.html - but specialized to our needs. */
+STATIC void vmg_sv_magicuvar(pTHX_ SV *sv, const char *uf, I32 len) {
+#define vmg_sv_magicuvar(S, U, L) vmg_sv_magicuvar(aTHX_ (S), (U), (L))
+ const MAGIC* mg;
+ sv_magic(sv, NULL, PERL_MAGIC_uvar, uf, len);
+ /* uvar magic has set and get magic, hence this has set SVs_GMG and SVs_SMG. */
+ PERL_UNUSED_CONTEXT;
+ if ((mg = SvMAGIC(sv))) {
+ SvRMAGICAL_off(sv);
+ do {
+ const MGVTBL* const vtbl = mg->mg_virtual;
+ if (vtbl) {
+ if (vtbl->svt_clear) {
+ SvRMAGICAL_on(sv);
+ break;
+ }
+ }
+ } while ((mg = mg->mg_moremagic));
+ }
+}
+
+#endif /* VMG_UVAR */
+
+/* --- Context-safe global data -------------------------------------------- */
+
+#define MY_CXT_KEY __PACKAGE__ "::_guts" XS_VERSION
+
+typedef struct {
+ HV *wizz;
+ U16 count;
+} my_cxt_t;
+
+START_MY_CXT
+
+STATIC void vmg_cxt_init
+#if defined(pMY_CXT) && defined(aMY_CXT)
+ (pTHX_ pMY_CXT) {
+# define vmg_cxt_init() vmg_cxt_init(aTHX_ aMY_CXT)
+#else
+ (pTHX) {
+ dMY_CXT;
+# define vmg_cxt_init() vmg_cxt_init(aTHX)
+#endif
+ MY_CXT.wizz = newHV();
+#ifdef USE_ITHREADS
+ HvSHAREKEYS_off(MY_CXT.wizz);
+#endif
+ MY_CXT.count = 0;
+ return;
+}
+
+/* --- Signatures ---------------------------------------------------------- */
+
+#define SIG_MIN ((U16) (1u << 8))
+#define SIG_MAX ((U16) ((1u << 16) - 1))
+#define SIG_NBR (SIG_MAX - SIG_MIN + 1)
+#define SIG_WIZ ((U16) ((1u << 8) - 1))
+
+/* ... Generate signatures ................................................. */
+
+STATIC U16 vmg_gensig(pTHX) {
+#define vmg_gensig() vmg_gensig(aTHX)
+ U16 sig;
+ char buf[8];
+ dMY_CXT;
+
+ do {
+ sig = SIG_NBR * Drand01() + SIG_MIN;
+ } while (hv_exists(MY_CXT.wizz, buf, sprintf(buf, "%u", sig)));